Gain G: amount of energy an isotropic antenna would radiated in the same direction when driven by the same input power. G = 4phA/l2 where A is the aperture, h is the efficiency, and l is the wavelength.

Polarization: must be compatibly with the radio wave.

3dB loss for linear/circular mismatch

25 dB loss (or greater) for right/left mismatch

Infinite loss for vertical/horizontal mismatch

Directive Gain

An antenna does not amplify. It only distributes energy through space to make use of energy available.

The noise temperature of the second stage is divided by the power gain of the first stage when referred to the input. Thus, in order to keep the overall system noise as low as possible, the first stage (usually an LNA) should have high power gain as well as low noise temperature.

For a digital system, the bit energy-to-noise ratio is related to the carrier-to-noise density as follows [Eb/ N0] = [C/N] + [B] – [Rb] = [C/ N0] –[Rb] where Rb is the bit rate and B is the noise bandwidth of the receiver.

The ratio Eb/ N0 is crucial in determining the bit error rate, which depends also on the digital modulation technique.

In practice,

The bit error rate is specified

The modulation scheme is determined and the corresponding Eb/ N0 is computed

When a series of input signals from different sources have to be transmitted along the same physical channel, multiplexing is used to allow several communication signals to be transmitted over a single medium.

Frequency division multiplexing (FDM)

FDM places multiple incoming signals on different frequencies. Then are they are all transmitted at the same time

The receiving FDM splits the frequencies into multiple signals again

Time division multiplexing (TDM)

TDM slices multiple incoming signals into small time intervals Multiple incoming lines are merged into time slices that are transmitted via satellite

The receiving TDM splits the time slices back into separate signals

FDM signal 1 FM modulator Summer FDM signal carrier f1

IRIG standard:

Proportional bandwidth (PBW): peak frequency deviation of the subcarrier is proportional to the subcarrier frequency

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